JP2011112511A - Magnetic type force sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a magnetic type force sensor capable of detecting and correcting accurately fluctuation of a generated magnetic field of a magnetic flux generation source. <P>SOLUTION: This sensor is provided with a displacement magnetoelectric conversion element (4) for detecting a magnetic field change generated by an external force so as to be faced to a magnetic pole end face of the magnetic flux generation source (5), and a fixed magnetoelectric conversion element (7) not generating a magnetic field change generated by the external force. A fluctuation ΔB of the generated magnetic field of the magnetic flux generation source generated by an environmental fluctuation such as a temperature rise inside the sensor, or by a secular change or the like is detected by the fixed magnetoelectric conversion element (7). Offset correction of the displacement magnetoelectric conversion element or correction of a sensitivity coefficient is performed by performing correction processing by an operation part (11) based on the detection amount. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a magnetic force sensor that detects a change in magnetic flux of a magnetic flux generation source using a magnetoelectric transducer, and more particularly to correction when a magnetic field generated by the magnetic flux generation source changes.

  For example, when a part is assembled by a robot arm, the force sensor is attached to the wrist portion and is used to detect a force or moment component generated during the assembling work and to control the posture of the hand unit. As the force sensor, a sensor using a method of magnetically detecting the displacement of the action part as described in JP-A-2004-325328 (Patent Document 1) is proposed.

  The structure of the conventional example described in Patent Document 1 is shown in FIG. The four magnetoelectric conversion elements 15a to 15d are arranged so as to face the permanent magnet 14 embedded in the elastic body and the magnetic poles of the permanent magnet 14. When an acting force is applied to the elastic body, the permanent magnet 14 is displaced, and changes in the magnetic field generated thereby are detected by the magnetoelectric conversion elements 15a to 15d such as Hall elements. Based on the detected change in the magnetic field, force components in the X-axis direction, the Y-axis direction, and the Z-axis direction can be detected.

  In Patent Document 1, a permanent magnet is used as a magnetic flux generation source. Generally, the absolute value of the strength of a magnetic field generated by a permanent magnet varies depending on the temperature of the permanent magnet (having a predetermined temperature coefficient). When the temperature of the permanent magnet rises due to heat generated from the circuit board, heat received from the outside such as a motor arranged around the permanent magnet, the strength of the magnetic field is weakened. Therefore, an apparatus using a magnetic field generated by a permanent magnet needs to compensate for a change in the magnetic field due to its temperature. In addition to the influence of temperature and the like, the magnetic field also changes due to aging of the permanent magnet.

  On the other hand, a method of performing temperature compensation by a temperature compensation circuit provided with a temperature sensor as in JP-A-2005-321592 (Patent Document 2) is employed.

The structure of the conventional example described in Patent Document 2 is shown in the figure. In FIG. 6A, the Hall element 16 provided at a position facing the permanent magnet 14 is depicted. FIG. 6B illustrates a temperature compensation circuit connected to a constant voltage source (not shown) provided adjacent to the Hall element.
When the output voltage from the Hall element to the selector drops due to a temperature rise, the negative temperature characteristic of the temperature sensor provided in the temperature compensation circuit provided adjacent to the Hall element is proportional to the temperature rise. The current value output from the temperature compensation circuit to the Hall element is increased.
By outputting this increased current to the Hall element 16, the output voltage from the Hall element 16 to the selector, which has been reduced due to the temperature rise, is recovered.

JP 2004-325328 A JP 2005-315992 A

  However, in the conventional example described in the cited document 2, temperature compensation is performed for the output of the Hall element that is a receiver of the magnetic flux. Therefore, when there is a difference in the heat capacity (specific heat) between the permanent magnet and the temperature sensor, or when the temperature rises locally, such as when the temperature of the permanent magnet 14 itself rises while there is no temperature change in the Hall element, the temperature sensor However, it is difficult to accurately measure the average temperature of the permanent magnet. Further, a temperature compensation circuit must be provided separately from a detector such as a Hall element or a permanent magnet, which is disadvantageous from the viewpoint of cost and miniaturization.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to provide a compact magnetic force sensor capable of accurately detecting and correcting fluctuations in a magnetic field generated by a magnetic flux generation source. Is to provide.

In order to solve the above problems, the present invention
In the magnetic force sensor that detects the force based on the relative position between the action part and the magnetic flux generation source that can be displaced by the force received by the action part,
An action part elastically supported by the support member;
A first magnetoelectric transducer fixed to the action part;
A magnetic flux generation source disposed opposite to the first magnetoelectric transducer;
A second magnetoelectric transducer disposed at a fixed position with respect to the magnetic flux generation source;
And an arithmetic processing unit that corrects the output of the first magnetoelectric conversion element based on the output of the second magnetoelectric conversion element.

  ADVANTAGE OF THE INVENTION According to this invention, the force sensor of a compact structure which does not use additional structures, such as a temperature compensation circuit, can be provided. Further, according to the magnetic force sensor of the present invention, it is possible to correct for fluctuations in the generated magnetic field of the magnetic flux generation source generated due to causes other than temperature fluctuations.

It is a figure which shows the structure of the magnetic type force sensor which concerns on this invention. It is a figure for demonstrating the temperature compensation method of this invention of this invention. It is the magnetic flux diagram which performed the simulation with the Z-axis symmetrical two-dimensional static magnetic field model. It is the magnetic flux diagram which performed the simulation with the Z-axis symmetrical two-dimensional static magnetic field model. It is a figure which shows the structure of the conventional magnetic type force sensor. It is a figure which shows the structure of the conventional force sensor.

  FIG. 1 is a drawing that best represents the features of the present invention, and is a cross-sectional view of the magnetic force sensor taken along the X-Z axis.

  In FIG. 1, 1 is an action part to which a force is applied, 2 is an elastic body that elastically supports the action part 1 on the housing, and the action part 1 is elastically supported so that it can be displaced when a force is applied to the action part. ing. 3 is a substrate for mounting the magnetoelectric conversion element, 4a to 4b are magnetoelectric conversion elements (hereinafter referred to as displacement magnetoelectric conversion elements), 5 is a magnetic flux generation source, 6 is supporting the magnetic flux generation source 5, and the magnetoelectric conversion element It is the board which mounts. Reference numeral 7 denotes a magnetoelectric conversion element (hereinafter referred to as a fixed magnetoelectric conversion element) provided on the mounting substrate 6 and having a fixed relative position to the magnetic flux generation source 5.

  The magnetic flux generation source 5 may be a permanent magnet represented by an Nd—Fe—B magnet, an Sm—Co magnet, an Sm—Fe—N magnet, or a ferrite magnet. It may be an electromagnet that generates a magnetic force. The fixed magnetoelectric conversion element 7 and the displacement magnetoelectric conversion elements 4a to 4b can output changes in the magnetic field as electric signals, such as Hall elements, MR elements, magnetic impedance elements, flux gate elements, and winding coils. Moreover, the action part 1 does not need to be supported with respect to a housing | casing, and the action part 1 should just be supported by the support member which can be supported via an elastic body.

  When a force is applied to the action part 1, the action part 1 is displaced with respect to the magnetic flux generation source 5 by elastic deformation of the elastic body 2 together with the mounting substrate 3 and the displacement magnetoelectric transducers 4 a and 4 b. Thereby, from the displacement magnetoelectric transducers 4a and 4b, an electrical signal change proportional to the amount of displacement is obtained as an output. On the other hand, the mounting substrate 6 to which the fixed magnetoelectric conversion element 7 is attached does not cause an electrical change in output even when a force is applied to the action portion 1. That is, when a change occurs in the output of the fixed magnetoelectric conversion element 7, there is a change in the amount of magnetic flux generated by the magnetic flux generation source 5 due to environmental fluctuations such as a temperature increase (or temperature decrease) or a secular change of the magnetic flux generation source 5. It is.

A method for calculating force and moment will be described with reference to FIG. For example, it is assumed that the acting portion 1 receives a force Fz in the Z-axis direction and a moment My in the Y-axis direction. Let B4a, B4b, and B7 be the amount of change in magnetic flux density that passes through the displacement magnetoelectric conversion elements 4a and 4b and the fixed magnetoelectric conversion element 7, respectively. kz and ky are sensitivity coefficients for calculating force and moment from the magnetic flux density displacement amount.
Fz = kz ((B4a + B4b) -B7)
My = ky (B4a-B4b)

  As described above, the force and moment applied to the action part 1 are calculated from the amount of change in magnetic flux density passing through the displacement magnetoelectric transducers 4a and 4b and the fixed magnetoelectric transducer 7 by taking the difference of each element. can do. Here, it is understood that the fixed magnetoelectric conversion element 7 functions not only as a temperature change described below but also as an output reference element in the force detection.

  Next, the temperature compensation method of the present invention will be described with reference to FIG. 4a and 4b are the displacement magnetoelectric conversion elements described above, and 7 is a fixed magnetoelectric conversion element.

  A signal amplifying unit 8 amplifies the signal of the magnetoelectric conversion element, and is connected to each magnetoelectric conversion element. Reference numeral 9 denotes a signal converter for taking an output signal from the magnetoelectric conversion element into the arithmetic unit, and is connected to the signal amplifying unit 8. Reference numeral 10 denotes a signal adjuster that feeds back to the displacement magnetoelectric conversion element based on the calculation result of the calculation unit, and outputs a signal for performing correction processing before the output of the displacement magnetoelectric conversion element is input to the converter 9. It can be configured.

  As a result of the fluctuation of the magnetic field generated by the magnetic flux generation source 5 by ΔB due to temperature fluctuation or secular change, the output voltage of the fixed magnetoelectric conversion element 7 changes by ΔV7 = ksΔB. Here, ks is a coefficient for converting the magnetic flux change amount into the output voltage. The process from the detection of the fluctuation of the generated magnetic field to the correction process is shown below.

<1. Detection of generated magnetic field fluctuations>
The fixed magnetoelectric conversion element 7 detects the output change caused by the fluctuation of the magnetic field generated by the magnetic flux generation source 5 through the converter 9 by the calculation unit.
The signal amplification factor of the signal amplification unit 8 is set to G times. When the output voltage of the fixed magnetoelectric conversion element 7 changes by ΔV7 due to the magnetic field fluctuation, the voltage output through the signal amplifier 8 changes by ΔVt = GΔV7. This change ΔVt is detected by the arithmetic unit through a converter including an A / D converter or the like. Thereby, the magnetic flux density changed from ΔB = ΔVt / ksG can be calculated. Here, the detection resolution of the converter must be capable of sufficiently detecting the change to be corrected.

<2. Correction of sensitivity coefficient>
When the magnetic field generated by the magnetic flux generation source 5 changes, the output of the magnetoelectric conversion element generated by the change in the relative position between the action unit 1 and the magnetic flux generation source 5 generated by an external force also changes.
Therefore, in order to calculate an accurate external force value from the output of the magnetoelectric conversion element, it is necessary to correct the sensitivity coefficients kz and ky of the sensor output according to the generated magnetic field. As described above, if the magnetic flux density before the change is B based on the changed magnetic flux change ΔB, the corrected sensitivity coefficient including the influence of the change in the generated magnetic field is {(B−ΔB) / B} ×. kz and {(B−ΔB) / B} × ky may be used. When there is no change in the generated magnetic field (ΔB = 0), the value of (B−ΔB) / B is 1, and the above sensitivity coefficients are kz and ky, respectively.

<3. Offset processing>
It is assumed that a change in the magnetic field generated by the magnetic flux generation source 5 changes ΔVt from the reference voltage value when the output of the fixed magnetoelectric conversion element 7 is input to the converter 9. Based on the difference ΔVt, the calculation unit calculates the offset ΔVoff of the displacement magnetoelectric transducer 4. The output voltage of the displacement magnetoelectric transducer 4 changes by ΔV4 = kdΔB, and ΔVoff = GΔV4. Here, kd is a coefficient for converting the magnetic flux change amount to the output voltage. Since ΔBt can be calculated from ΔVt as described in the item of detection of the generated magnetic field fluctuation, ΔVoff can be calculated. The regulator 10 feeds back to the signal amplifying unit 8 connected to the displacement magnetoelectric transducers 4a and 4b so as to cancel this ΔVoff. Thereby, based on the output of the fixed magnetoelectric conversion element 7, the offset of the displacement magnetoelectric conversion element 4 can be corrected in real time. In addition, when the amount of magnetic field fluctuation generated by the magnetic flux generation source 5 is slight with respect to time change and correction is not necessary in real time, the reference voltage value of the displacement magnetoelectric transducer (the voltage when no external force is applied to the action unit 1) You may make it cancel the difference from (value).

  The signal range that can be input to the converter 9 is determined to be a specific range. Therefore, if an offset occurs in the output of the displacement magnetoelectric transducer, the range that can be detected by the sensor is narrowed. The offset processing described above is also meaningful in order to appropriately use the signal range that can be input to the converter 9.

<4. Output calculation processing>
On the other hand, a calculation formula including correction of the generated magnetic field variation is shown as follows. Here, kp = (B−ΔB) / B is a correction sensitivity coefficient.
Fz = kp × kz ((B4a + B4b) −B7)
My = kp × ky (B4a-B4b)
It can be seen that the offsets of the displacement magnetoelectric transducers 4a and 4b are adjusted before the electric signal is input to the converter 9, and therefore do not affect the calculation performed by the calculation unit 11. Therefore, it is possible to easily correct the fluctuation of the generated magnetic field by simply multiplying the correction sensitivity coefficient as compared with the case where correction is not performed, and to calculate an accurate external force and moment.
Further, since the method of the present invention corrects the sensitivity coefficient based on the generated magnetic field itself generated by the magnetic flux generating source, other than temperature, such as a change in the generated magnetic field due to secular change that could not be corrected by the method using the conventional temperature compensation circuit. It can also cope with changes in the generated magnetic field caused by

  As already described, in a magnetic force sensor, it is desired to accurately detect an output change caused by an external force and an output change caused by a change in the magnetic field generated by the magnetic flux generation source 5. For this purpose, it is important to dispose the magnetoelectric conversion element at a location where the change amount of the magnetic flux is most easily detected. We studied for that.

  3 and 4 show the results of the magnetic field simulation. The simulation was performed with a two-dimensional static magnetic field model related to the magnetic flux generation source 5 symmetric with respect to the Z axis. Since the generated magnetic field is also symmetrical, the center line of the magnetic pole is drawn at the left end in FIGS. 3 and 4 and only the right half is shown.

In FIG. 3, a magnetic flux generation source 5 having a thickness of 4 mm in the Z-axis direction and a thickness of 2 mm in the X-axis direction is arranged in the air. FIG. A 1 mm magnetic body 13 is wound.
Here, the characteristics of an Nd—Fe—B magnet having a residual magnetic flux density of 1.4 T and a coercive force of 1000 kA / m were set as the magnetic flux generation source, and the relative permeability of the magnetic material was set to 5000.

  The place where the amount of change in magnetic flux is the maximum is the place where the magnetic flux lines are the densest. The magnetic flux source 5 alone (FIG. 3) and a magnetic body capable of controlling the flow of magnetic flux were installed (FIG. 4). From any of these results, the location where the magnetic flux lines are the densest, that is, the location where the amount of change in the magnetic flux can be obtained most It is understood that the magnetic flux generation source 5 is near the magnetic pole end face.

  Based on this result, the arrangement locations of the fixed magnetoelectric transducers 4a and 4b and the displacement magnetoelectric transducer 7 are examined. It is difficult to mount the fixed magnetoelectric conversion element and the displacement magnetoelectric conversion element on the same substrate. Therefore, the substrate for mounting the fixed magnetoelectric conversion element and the displacement magnetoelectric conversion element must be separated, and at least two substrates are required.

  Magnetic flux lines are dense in the vicinity of the two magnetic poles (N pole and S pole) of the magnetic flux generation source. If a magnetoelectric transducer is provided in the vicinity of the magnetic pole, changes in relative displacement with the magnetic flux generation source can be detected sensitively. I found out that I can do it.

  In particular, as shown in FIGS. 3 and 4, when the pole of the rod-shaped magnetic flux generation source 5 has an end face, the fixed magnetoelectric conversion element 7 is fixed to the end face of one of the magnetic poles, and the displacement magnetoelectric conversion elements 4a and 4b are It can arrange | position in the position facing the other magnetic pole. It can be seen that such a configuration is a structure that can detect the force and the fluctuation of the generated magnetic field of the magnetic flux generation source with the highest accuracy.

  The present invention is suitable as a force sensor used in an industrial robot arm.

DESCRIPTION OF SYMBOLS 1 Action part 2 Elastic body 3 Displacement magnetoelectric conversion element mounting board 4a-4b Displacement magnetoelectric conversion element 5 Magnetic flux generation source 6 Fixed magnetoelectric conversion element mounting board 7 Fixed magnetoelectric conversion element 8 Signal amplification part 9 Signal conversion part 10 Signal adjustment part DESCRIPTION OF SYMBOLS 11 Calculation part 12 Magnetic flux line 13 Magnetic body 14 Permanent magnet 15a-15b Magnetoelectric conversion element 16 Hall element

Claims (4)

In the magnetic force sensor that detects the force based on the relative position between the action part and the magnetic flux generation source that can be displaced by the force received by the action part,
An action part elastically supported by the support member;
A first magnetoelectric transducer fixed to the action part;
A magnetic flux generation source disposed opposite to the first magnetoelectric transducer;
A second magnetoelectric transducer disposed at a fixed position with respect to the magnetic flux generation source;
A magnetic force sensor comprising: an arithmetic processing unit that corrects an output of the first magnetoelectric conversion element based on an output of the second magnetoelectric conversion element. An adjuster for feeding back the calculation result of the calculation processing unit to the first magnetoelectric transducer;
The offset of the first magnetoelectric conversion element calculated based on the difference between the predetermined reference voltage value and the voltage value due to the output of the second magnetoelectric conversion element when no external force is applied to the action portion The magnetic force sensor according to claim 1, wherein feedback for canceling is performed on the output of the first magnetoelectric transducer. An adjuster for feeding back the calculation result of the calculation processing unit to the first magnetoelectric transducer;
When the magnetic field generated by the magnetic flux generation source is B, and the fluctuation of the magnetic field generated by the magnetic flux generation source calculated based on the output of the second magnetoelectric conversion element is ΔB, the output of the first magnetoelectric conversion element is 2. The magnetic force sensor according to claim 1, wherein feedback of (B- [Delta] B) / B times is performed.   The second magnetoelectric conversion element is disposed near one magnetic pole of the magnetic flux generation source, and the first magnetoelectric conversion element is provided near the other magnetic pole of the magnetic flux generation source. 2. A magnetic force sensor according to 1.

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